Description:

Objective:

The objective of this research project is to
develop a receptor-based modeling technique to improve characterization of
known sources of groundwater
contamination, and to identify previously unknown sources of groundwater contamination.

Approach:

The governing equation for source-based mathematical
models of contaminant transport in groundwater is the advection-dispersion
equation (ADE), with the
contaminant concentration as the state variable. The source-based ADE can be
used to estimate the concentration of the contamination as a function of location
and time after release from the source. Receptor-based models use a similar
governing equation called the adjoint of the ADE. In the adjoint equation,
location or travel time probability is the state variable; therefore, these
probabilities are adjoint states of concentration. In the source-based model,
the flow of information is downgradient, away from the source; in the receptor-based
model, the flow of information is upgradient, away from the receptor and towards
possible sources. To account for this reversal of flow, the sign on the advective
term in the adjoint equation is reversed, and the receptor is a source of probability
in the adjoint equation. The governing equation and boundary and initial conditions
of the receptor-based model can be developed from adjoint theory. If contamination
is detected at one receptor, the adjoint equation can be solved to obtain a
distribution of location or travel time probability. If contamination is detected
at multiple receptors, each receptor can be modeled as a source of probability
in the adjoint equation; however, the equation does not account for the correlation
between the detections. If the contamination parcels that are detected at the
two receptors originated from the same source, the transport of the parcels
is correlated. Therefore, the adjoint equation must be modified to account
for the correlation of the two detections. With two correlated detections,
the spread of the probability distributions should be smaller than the spread
of the distribution with only one detection. The information from additional
detections is expected to reduce the variance of the probability distribution,
providing a better estimate of the source location.

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.